Modified AASHTO empirical pavement design method for geosynthetic-reinforced asphalt

Geosynthetics are commonly adopted to retard problems associated with reflective cracking in asphalt, although their inclusion as asphalt reinforcements also provides structural benefits. However, methodologies are yet to develop to incorporate these structural benefits into design. This study proposes a design method to account for structural capacity increase by geosynthetics in asphalt. The proposed method relies on quantifying a tensile strain reduction ratio (α) defined as the ratio between elastic tensile strain in HMA in a geosynthetic-reinforced asphalt road and that in an equivalent unreinforced road. Implementation of the design method involves incorporating a modified structural number or modified ESAL into AASHTO1993 design by using an equivalent modulus or an equivalent axle load factor for asphalt-geosynthetic composite. The geosynthetic benefits were ultimately accounted for in design either by reducing the asphalt thickness or by increasing the traffic volume. This paper presents the results of parametric evaluations of geosynthetic benefits for α ranging from 0.8 to 0.4. Design charts were developed to facilitate adoption of the proposed design method, and a design example is provided to illustrate the predicted benefits. It was found that 20% to 33% reduction in asphalt thickness, or 1.8- to 4.0-fold increase in traffic volume, is feasible.